Notes on the population of Luperina nickerlii leechi Goater (Lepidoptera: Noctuidae) at its site in Cornwall, 1987 to 1989

5 Pages·1991·1.6 MB·

by  A Spalding

BR. J. ENT. NAT. HIST.,4: 1991 133
NOTES ON THE POPULATION OF LUPERINA NICKERLIILEECHI
GOATER (LEPIDOPTERA: NOCTUIDAE) AT ITS SITE IN
CORNWALL, 1987 TO 1989
Adrian Spalding
Lerryn Cottage, Lerryn, Lostwithiel, CornwallPL22 OQB.
Introduction
Luperinanickerlii(Frey.)(thesandhillrustic)hasfourdistinctpopulationsinBritain.
The nominate subspecies is found in Essex, and there are three subspecies living in
coastal areas in North Wales and Lancashire, in Ireland, and in Cornwall. The
subspecies in Cornwall is Luperina nickerlii leechi, which was discovered in 1974
(Goater, 1976)onastripofshinglysandabout500metreslongand240metreswide.
The moth has silvery grey forewings marked with a dark brown median band. The
subspeciesinNorthWales(gueneeiDoubl.)ispaler, whilsttheIrishsubspecies(knilli
Boursin) is dark brown. The nominate species is widespread over Europe, with two
subspeciesgraslini(Obth.) and tardenota(J. Joan.) (Leraut, 1980). Some examples
ofLuperinanickerliinickerliiweretaken at Bradwell in Essexwhich were originally
thought to be migrants, but it has now been shown that the species is resident from
CanveyIslandtoHarwich(Emmet&Pyman, 1985)andtheIsleofSheppey(Skinner,
1985). It may be that L. nickerliimigrates, as an unnamed subspecies was found at
Farringdon on 22.ix.1950 (Goater, 1974) and a single female (the nominate form)
was found at Bude in Cornwall on 6.viii.1990 by David Wedd and exhibited at the
1990 BENHS exhibition (Wedd, 1991).
Anaccount ofthebiologyofLuperinanickerliileechiisgiveninHeath&Emmet
(1983). Theownersofthesitehaverequestedthatitsnameandlocationbekeptsecret.
Aims and methods
The aim was to estimate the population and distribution of the adult stage of
Luperina nickerlii leechi at its site in Cornwall.
Populationcounts ofmothsareusuallymadewithmark/release/recaptureschemes,
using light traps as the means ofcapture. This method works very well with moths
thatfly, but, byrepute,L. nickerliirarelyfliesanddoesnotcometolight. Thehabitat
was divided into 14 areas of equal width, marked off with bamboo poles, and the
position of each moth was recorded. The moths could be seen at night resting on
thestemsofthefoodplant,Elymusfarctus, andwereeasilycaught. Thebestmethod
wastokneelontheshingle, gettingdownto 'moth-level', andtosweeptheareawith
apowerfulquartz-halogensearchlight. Themothswereeasilyseenthisway, especially
when the searchlight reflected in their eyes. Each moth caught was marked on its
forewingwithredfelt-tippen. Eachmarkonthewingrepresentedadifferentnumber
(1, 2,4, 7, 10, 20,40, 70, 100, 200)accordingtoitsposition, sothatupto454moths
could be individually marked. The number of males, females and pairs was noted
and all recaptures were recorded. In the first year, the whole habitat was searched,
including those areas without the foodplant. The habitat was too large to search in
onenight. Ontwo occasions (24&25.viii.1987 and 28 &29.viii.1987), the whole of
the area was searched on two successive nights in order to get an idea of the total
population.
In 1988, two attempts were madeto attract themoths to light, on 4.ix.l988 using
aportableHeathtrapandon7.ix.l988 usinga 125-wattm.v. lampon awhitesheet.
,34 BR. J. ENT. NAT. HIST.,4: 1991
Results
Table 1. Numbers of Luperina nickerlii leechi on site, 1987-1989.
Year Males Females Pairs Total
987
BR. J. ENT. NAT. HIST.,4: 1991 135
the other half. The population on these two nights may have been as low as 24. In
1988, the whole habitat was searched twice; 20 moths were found on 2.ix.l988 and
35 moths on 3.ix.l988. In 1989, only the most productive areas were searched;
69 moths were found on 30.viii.1989 and 74 moths on 31.viii.1989.
The relative emergence dates ofmales and females is shown in Table 2. In 1987,
the first males were found 10days beforethe first female, whereasin 1988 a female
wasfound6daysbeforethefirstmale. In 1989femalesandmaleswerefoundtogether.
Malesformed62.67% ofthetotalin 1987, 50.57% in 1988butonly30.62% in 1989.
The number ofrecaptures was very low. There was 1 recapture (a male) in 1987
out of 76 moths, 6 recaptures (4 males, 2 females) in 1988 out of 87 moths and 1
moth was recaptured twice. Six of these recaptures were at light (2 to tilley lamp,
4totheHeathtrap). Fourwererecapturedonthe followingnight, 1 wasrecaptured
on the same night, and 1 was recaptured 2 nights later. There were 5 recaptures (1
male, 4 females) in 1989, 1 on the same night, 4 on the succeeding night. One male
with crumpled wings was captured at the same place the following night and may
not have moved in this time.
On 4.ix.l988 39 moths were caught in the Heath trap placed near the centre of
thesite. Theslightwind(possiblyforce2)decreasedduringthenight. Theminimum
temperaturewas 13.5°Cat06.45a.m.L. nickerliiwasthemostcommonmothcaught,
with 1 recaptured female, 3 recaptured males and 16 fresh males, 2 ofwhich were
darker than usual. The next most common moth was Luperina testacea (O. & S.)
(15 caught). On 7.ix.l988, an m.v. lamp was run on a white sheet from 22.50p.m.
to 12.10a.m. No L. nickerlii were caught. Several Diptera and Trichoptera were
attractedtothelight,aswellascrawlingopiliones,inadditiontothemothsAutographa
gamma (L.), Tholera decimalis (Poda), and Luperina testacea (2).
Discussion
Inmanymark/release/recaptureschemes, suchasBailey'striplecatchmethodand
theLincolnindexmethod, thepopulationisrequiredtobewellmixedaftermarking
beforepopulationestimatescanbemade(Southwood, 1978). Thesemethodsprovide
an estimate ofthe total population, includingthosemoths present but not seen. As
themothsrarely fly, mixingtheL. nickerliipopulationwasdifficultandthesemethods
wereunsuitable. Onemothwasseenthefollowingnightapparentlynothavingmoved.
Markingthespecimensprovidedanactualhabitatcount, withnoestimateofpossible
total numbers.
Thetotalsof75, 87, 209fortheyears 1987-1989arenumbersrecorded. Theactual
totals in these years may have been much higher. The colony was only sampled on
afewnightsduringtheflightperiod,e.g. in 1987thecolonywassampledon 10nights
in a flight period of at least 27 nights. The population may have been three times
higher than recorded. The flight season is a long one. The first and last sightings
were 2 males on 14.viii.1987 and 1 male on 24.ix.1989.
Thenumberofrecaptures(12in3years)wastoolowforanyestimatesofpopulation
size to be made from these figures. Six of the recaptures were to light. The low
recapturerateis puzzlingand thereare several possibleexplanations, (a) Themoths
may have a very short lifespan. One moth caught in 1988 was recaptured twice and
was the only moth shown to live for over 2 days, (b) A high proportion of those
mothspresentcouldhavebeenoverlooked, includingmarkedspecimens(mytechnique
improved with practice), however, the marked moths were easier to see than the
unmarked ones, (c) The survey methods may have affected the results and marked
moths may have beenmoreproneto predation. (d) Some moths mayhavemigrated
136 BR. J. ENT. NAT. HIST.,4: 1991
or have been blown by strong winds from the site. This is unlikely, as the species
seems well adapted to its wind-swept habitat.
Numbers found varied from night to night (dropping from 35 on 3.ix.l988 to 21
on 4.ix.l988). Emergence rates might be erratic and vary according to unknown
factors. Strong winds may keep moths clinging to Elymusfarctus stems, but fewer
moths (20) were caught on 2.ix.l988 in a strong wind than on 3.ix.l988 in a light
wind (35 moths caught). Peak numbers (74) were found on 31.viii.1989, when only
themostproductiveareasweresearched,andthetotalpopulationwasprobablyhigher
than this.
Between 1987 and 1989 total numbers increased considerably (from 75 to 209).
Part of the habitat had been affected by construction work in 1986, when a large
area of Elymusfarctus had been bulldozed away. By 1989, Elymusfarctus had
recolonized this area and moth numbers here increased from 12 (16%) in 1987 to
101 (48.33%)in 1989. ThepopulationofL.n. leechiseemstovaryfromyeartoyear.
Details ofmoth records provided by Colin Hart show that 60 moths were found on
23.viii.1975 and on 28.viii.1984, whilst 50moths wererecorded in under 30minutes
on 29.viii.1981. In 1976, G. Senior recorded about 150 moths in 1 hour. I know of
no records for 1980, when accordingto Colin Hart littlevegetationwas visible. The
subspecies seems to do well in hot, dry summers such as 1976 and 1989.
With several moth species, it is usual for the males to emerge before females and
for males to be more common than females. However, with some species living in
difficult environments or when the females fly little or are immobile, the females
mayemergefirst(Novak, 1980). In 1987 2maleswere found 10daysbeforethe first
female, but in 1988 afemalewas found first. In 1989 females andmaleswere found
together, andnopatterncanbereadintothesefigures. Theproportionofmalesseen
declined between 1987and 1989. Thetotals for 1988include 16malescaughtatlight.
Ifwesubtractthiscatchfromthe 1988total, theproportionofmalesin 1988(32.18%)
isclosetothe 1989proportion (30.77%). These figures do not includeflyingmoths,
many ofwhich arelikelyto havebeen males. Furtherresearch is neededtoestablish
the mean ratio of males to females.
In 1988, 21% ofthe catch consisted of mating pairs. It may be that pairing only
takes place when the weather conditions are suitable. The minimum temperatures
on the2nights when pairingwas observed were9°Cand 8°C respectively, although
the first nightwas verywindy. Nopairing was observed beforemidnight, or in 1987
and 1989.
Conclusion
ThenumbersofL.n. leechivaryfromyeartoyear. TheregrowthofElymusfarctus
on part of the site has been followed by an increase in the moth population. The
population seems to increase in hot, dry summers. The peak population seems to
be at the end of August. The low numbers of recaptures is puzzling and suggests
that a large number of moths may have been missed in the survey.
Acknowledgements
I am grateful for the assistance ofMary Atkinson, Loveday Jenkin, Lyn Jenkins
and Rosann Sparshott in searching for the moths, and to Stephen Church,
Colin Hart, Bernard Skinner and Martin Warren for their helpful comments. I am
particularly grateful to the owners of the site and their staff for their help and
advice.
br. j. ent. nat. hist.,4: 1991 137
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BOOK REVIEWS
Blackflies(Simuliidae), byI.A. Rubtsov. FaunaoftheUSSR.Vol. 6,Part6. Second
edition, 1956. English translation by Dr B. R. Sharma for Oxonian Press Pvt Ltd,
New Delhi, 1990, 1042 pp. Distributed by E. J. Brill, Leiden, 300 Dutch Guilders.
Ageneralintroductoryaccountisgivenonthebiologyofthisgroupofblood-sucking
flies, whichareaprominentcomponentoftheinsect faunainboreal andsub-boreal
regions and implicated in transmission of diseases of domestic animals.
Descriptionsand keysareprovided(toallstageswhereknown) forthe280species
recorded fromtheUSSR at thetimeofwriting and48 species known from adjacent
parts of Europe. The text is well illustrated with diagnostic features of all stages.
Information on distribution is supplemented by discussion ofthe biogeography of
genera and species groups.
Rubtsov (or Rubzov as his name is otherwise rendered in English) continued to
workonthegroupandhasdescribedmanyadditionalspeciesintheinterveningyears
since publication ofthe Russian edition. He contributed the keys to the Palaearctic
species published in Lindner's 'DieFliegen' series (1959-1964) and was a co-author
of the list for the family in the recent Palaearctic catalogue (1988), from which it
can be gleaned that morethan 400species ofSimuliidae arenow recorded from the
Soviet Union. In the British Isles we have only 35 species recorded, of which only
23 are dealt with in this work so it is of limited usefulness for identification ofthe
British fauna.
This work was, nevertheless, a thorough synthesis of information on the group
andincludesafulllistofreferencesupto 1955.Althoughnotuptodatetaxonomically
itprovidesagoodsummaryofknowledgeofthefamily,andabasisforfurtherstudies.
P. J. Chandler
Zoologia Neocaledonica. Volume 2 Memoires du Museum national d'Histoire
naturelle, Paris. Ser. A, tome 149, 1991, 358 pp, Edited by J. Chazeau & S. Tillier,
155 Dutch Guilders, available from Universal Book Services, Dr W. Backhuys,
Warmonderweg 80, 2341 KZ Oegstgeest, The Netherlands (mainly in French, some
—
chaptersinEnglish). Thisincludeschapters 15-32oftheresultsofFrenchexpeditions
to New Caledonia. Each is acontribution on adifferentgroup ofanimals; most are